The present invention relates to a portable circular saw having a rotatably driven circular saw blade, and more particularly, to a type having an arrangement for controlling a lateral inclination angle of a circular saw blade with respect to a base.
A conventional portable circular saw is shown in FIGS. 14 and 15. The conventional portable circular saw 101 includes a base 10 arranged in opposition to a workpiece to be cut, and a main body 120 pivotally movably supported to the base 10. The base 10 is placed on the workpiece during cutting operation.
The main body 120 rotatably supports a circular saw blade 21. The saw blade 21 is rotatable about an axis of a saw blade shaft 21A. The main body 120 houses therein an electric motor (not shown) and a power transmission mechanism (not shown) for rotatably driving the circular saw blade 21. Further, a main handle 22 is provided at a top end of the main body 120, and a subordinate handle 23 is provided at a front side of the main body 120. The term “front” and “rear” will be referred to in connection with a cutting direction. A saw cover 124 is provided integrally with the main body 120 for covering an upper half of the circular saw blade 21. Further, a safety cover (not shown) is provided pivotably movably about the saw blade shaft 21A for covering a lower half portion of the circular saw blade 21 during non-operating state. The safety cover is provided with a safety cover lever 25. A user can manually hold the safety cover lever 25 at its suitable angular position for maintaining a pivot position of the safety cover. When cutting a workpiece W from its rear end to its front end, the safety cover is automatically pivotally moved about the saw blade shaft 21A to automatically expose the lower half region of the circular saw blade 21 to an atmosphere. On the other hand, if the circular saw is to be moved from the front end to the rear end of the workpiece for forming a window or a frame hole, the safety cover lever 25 is latched by a user's finger to maintain an open state of the safety cover.
A slant position fixing member 111 upstands from the base 10. The slant position fixing member 111 is positioned at a front side of the base 10 and is provided with a scale or a gauge indicating an inclination angle of the circular saw blade 21 with respect to the base 10. A tiltable plate 126 is provided integrally with the front side of the saw cover 124 and at a position in confrontation with the slant position fixing member 111. The tiltable plate 126 is pivotally movably supported to the slant position fixing member 111 through a pin 12. The pin 12 extends in parallel with the base 10 and in a direction perpendicular to the saw blade shaft 21A. Therefore, the main body 120 is pivotally movable about the pin 12 between its upstanding position shown in FIG. 14 and a slanting position shown in FIG. 15.
The slant position fixing member 111 is formed with an arcuate slot 111a whose center of radius is coincident with an axis of the pin 12 serving as a pivot shaft of the tiltable plate 126. A fastening unit 30 is provided for fixing the pivot position of the tiltable plate 126 with respect to the slant position fixing member 111 when a tilting angle of the circular saw blade 21 with respect to the base 10 becomes a desired angle. The fastening unit 30 includes a thread and a lever 31. The thread penetrates through the arcuate slot 111a and threadingly engages the tiltable plate 126. The lever 31 is provided at one end of the thread. A base end face of the lever 31 serves as a pressure surface. In accordance with the threading advancing and retracting movement of the thread in accordance with the pivotal movement of the lever 31, the pressure surface of the lever 31 presses against the slant position fixing member 111 or is released therefrom. Because the lever 31 is provided, the thread can be rotated with a reduced force without employing a tool. The lever 31 is directed in parallel with the base 10 when the circular saw blade 21 is directed perpendicular to the base 10.
In use of the portable circular saw 101, when the circular saw blade 21 is directed perpendicular to the base 10 as shown in FIG. 14, the main body 120 is pressed against the workpiece W while the main handle 22 and the subordinate handle 23 are gripped by a right hand and a left hand, respectively. Then the base 10 is slidingly moved frontwardly on the workpiece W. In this case, an area of the workpiece in immediately front of the circular saw blade 21 can easily be observed, since the lever 31 is directed in substantially parallel with the base 10. Therefore, the user can perform cutting operation while acknowledging an inked marking line M. Further, an operator's finger pressing the subordinate handle 23 does not abut against the lever 31.
On the other hand, if an angled cutting as shown in FIG. 15 is to be performed, the lever 31 is temporarily unfastened for allowing the main body 120 to be pivotally moved, about the pin 12, relative to the base 10 so as to provide a desired tilting angle θ of the circular saw blade 21 with respect to the base 10. With this pivotal movement, relative position of the tiltable plate 126 with respect to the slant position fixing member 111 is changed. Then, the lever 31 is fastened to fix the posture of the tiltable plate 126 to the slant position fixing member 111. Consequently, tilting angle θ of the circular saw blade 21 is fixed.
However, in case of the angled cutting shown in FIG. 15 with the conventional portable circular saw, the lever 31 upon completion of fastening does not horizontally extend but rises up at its free end in accordance with the tilting angle θ of the circular saw blade 21, because pivotal amount to the complete fastening is uniform. The rising up lever 31 may interrupt a sight for observing the inked marking line M which is a guide line for cutting. Accordingly, a cutting direction cannot be accurately understood by the operator. Moreover, the operator's finger holding the subordinate handle 23 may be pressed against the rising lever 31. That is, the lever 31 becomes an obstacle for a smooth cutting operation.
In order to prevent the finger from being abutted against the lever 31, the subordinate handle 23 must be displaced rearwardly, i.e., must be positioned closer to the main handle 22. However, with such an arrangement, force imbalance may occur for holding the portable circular saw 101, and further, operability of the portable circular saw 101 in case of forming a window may be remarkably degraded. To be more specific, in cutting operation for forming a window, the safety lever 25 must be manually held at a frontward pivot position as shown in FIG. 14. Here, a hand of a finger that hold the safety cover lever 25 also holds the subordinate handle 23. Therefore, if the subordinate handle 23 is disposed close to the main handle 22, it becomes impossible to hold the safety cover lever 25 at its frontwardly shifting position by the finger of the hand while that hand also holds the subordinate handle 23. Consequently, a desirable cutting operation for forming a window cannot be performed.
Further, the subordinate handle 23 is preferably positioned spaced away from the circular saw blade 21 in the axial direction of the saw blade shaft 21A so as to easily observe the circular saw blade 21 when the operator looks down and peeps into the circular saw blade 21. However, due to the spaced away location of the subordinate handle 23, the rising-up free end of the lever 31 may abut the subordinate handle 23 to lower operability of the subordinate handle 23.